Universal mobile telecommunications system (UMTS) is a 3rd generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). The long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.
A closed subscriber group (CSG) identifies subscribers of an operator who are permitted to access one or more cells but which have restricted access (CSG cells). A CSG cell broadcasts a CSG indicator set to true and a specific CSG identity. A CSG whitelist is a list stored in a UE containing CSG identities of the CSG cells to which the subscriber belongs.
Due to an in-device industrial, scientific and medical (ISM) transmitter, a 3GPP LTE radio can be interfered in case that the 3GPP LTE radio and an ISM radio coexist within the same device operating in adjacent frequencies. It may be called as in-device coexistence (IDC) interference. For example, when the LTE radio is working on band 40 and the ISM radio such as wireless local area network (WLAN) is active in a same device at the same time, the LTE radio in Rx mode is interfered by the ISM transmitter. Also, the transmission of the LTE radio can interfere the reception of the ISM/GNSS (global navigation satellite system) radio.
The 3GPP LTE can provide a multimedia broadcast/multicast service (MBMS) service. The MBMS is a service which simultaneously transmits data packets to multiple users. If a specific level of users exists in the same cell, the respective users can be allowed to share necessary resources so that the plurality of users can receive the same multimedia data, thereby increasing resource efficiency. In addition, a multimedia service can be used with a low cost from the perspective of users.
When a UE is served by a CSG cell, there is a situation that the UE does not prefer the current serving CSG cell due to the IDC interference and/or the MBMS service. Accordingly, a method for performing a handover from the current serving CSG cell when the UE does not prefer the current serving CSG cell is required.